arXiv subjects

Urs Schreiber

Publications and source records attributed to Urs Schreiber.

111 records · Page 7Linked to original sources

arXiv2004

On deformations of 2d SCFTs

Motivated by the representation of the super Virasoro constraints as generalized Dirac-K{ä}hler constraints $(d \pm d^\dagger)|ψ> = 0$ on loop space, examples of the most general continuous deformations $d \to e^{-W} d e^W$ are considered which preserve the superconformal algebra at the level of Poisson brackets. The deformations which induce the massless NS and NS-NS backgrounds are exhibited. Hints for a manifest realization of S-duality in terms of an algebra isomorphism are discussed. It is shown how the first order theory of 'canonical deformations' is reproduced and how the deformation operator $W$ encodes vertex operators and gauge transformations.

hep-th↗

arXiv2004

Discrete Differential Geometry on causal graphs

Differential calculus on discrete spaces is studied in the manner of non-commutative geometry by representing the differential calculus by an operator algebra on a suitable Krein space. The discrete analogue of a (pseudo-)Riemannian metric is encoded in a deformation of the inner product on that space, which is the crucial technique of this paper. We study the general case but find that drastic and possibly vital simplifications occur when the underlying lattice is topologically hypercubic, in which case we explicitly construct mimetic analogues of the volume form, the Hodge star operator, and the Hodge inner product for arbitrary discrete geometries. It turns out that the formalism singles out a pseudo-Riemannian metric on topologically hypercubic graphs with respect to which all edges are lightlike. We study such causal graph complexes in detail and consider some of their possible physical applications, such as lattice Yang-Mills theory and lattice fermions.

math-ph↗

arXiv2004

Covariant Hamiltonian evolution in supersymmetric quantum systems

We develop a general formalism for covariant Hamiltonian evolution of supersymmetric (field) theories by making use of the fact that these can be represented on the exterior bundle over their bosonic configuration space as generalized Dirac-Kaehler systems of the form $(d \pm d^†)\ketψ = 0$. By using suitable deformations of the supersymmetry generators we find covariant Hamiltonians for target spaces with general gravitational and Kalb-Ramond field backgrounds and discuss their perturbation theory. As an example, these results are applied to the study of curvature corrections of superstring spectra for $AdS_3 x S^3$ close to its pp-wave limit.

hep-th↗